Three Stage Evaporative cooling unit

Schematic diagram of a multistage evaporative cooling system. A multi stage evaporative cooling system can work according to the humidity of ambient and humidity desired for supply air. When the relative humidity of ambient air is high, only indirect cooling can be used. This reduces the air temperature of supply air, but the humidity remains unchanged. When increase in humidity is also desired, as in dry hot seasons, direct evaporative cooling can be used

Evaporative cooling is a mechanism traditionally used to provide thermal comfort in hot and dry regions. The mechanism involves sensible and latent cooling of air with water. Direct evaporative cooling is most effective when the outside condition is dry and below the desired conditions. Indirect evaporative system is used during the seasons when little or no humidification is required i.e. when outside air humidity is within a comfortable range. Fresh filtered air is made to pass through a dry section of the system to cool the air through sensible heat transfer. Stage wise evaporative cooling systems can be either two stage or three stage.

• Two stage evaporative cooling systems (direct + indirect) – the direct system could be functional during the dry season, when humidification of air is required, and indirect system can be used when air primarily needs to be cooled.
• Three stage evaporative cooling system (direct + indirect + cooling coil) consists of direct and indirect evaporative cooling together with conventional cooling coil. The addition of cooling coils (chilled water or refrigerants) is helpful in monsoon season when the humidity level is high and dehumidification is required. Fresh air passed through the coils controls both sensible and latent heat requirements. The coils are also useful in winter season when some heating is also required.

The drawback of the two stage system is the high humidity level of the supply air. Over a period of time indirect evaporative cooling systems which provide sensible cooling of the air without humidification have emerged in the market.

Table:Advantages and disadvantages of evaporative cooling systems

An Efficiency Benchmark for the Building Industry

An Efficiency Benchmark for the Building Industry

Introduction

Buildings account for over one third of global energy consumption and are responsible for
an equally significant amount of carbon dioxide (CO2) emissions. In the Indian context,
with rapid urbanization and growing energy demand, it is essential to make sure that the
upcoming building stock is built in the most efficient way. The fact that 70% of the India
of 2030 is yet to be built provides a great opportunity for the building industry fraternity
to transform the way buildings are designed and to adopt a sustainable approach. Though
renewable energy sources like solar photovoltaic (PV) are getting cheaper by the day and
are witnessing tremendous growth, it is important to understand that the first step to being
sustainable is to bring down the demand (energy, water, materials, etc.) through resource
efficiency measures, and the second step is to meet the demand through renewables,
recycling, etc.
While the building industry embarks on the path of efficiency, it helps to have a
building efficiency benchmark to guide design and operations. The benchmark should
be unreasonable and challenging, but at the same time practically achievable. One such
benchmark is the Infosys EC-53 building, which was inducted into the ACREX Hall of
Fame in 2017.

Building Features

The Infosys EC-53 building, located in Electronics
City, Bengaluru is a combination of innovation
and excellence in building design and operation.
Sustainability measures were an integral part of the
design right from the concept stage, and included
the building envelope, innovative cooling system,
energy metering, automation and continuous
performance monitoring. The salient features of the
building are described below.
Pushing the Envelope
Building envelope is the most important aspect
of an efficient building design and can impact up to
50% of cooling demand. While most critics would
vote against insulation in a moderate climate like
Bengaluru, the EC-53 building has a fully insulated
high performance envelope. This includes insulated
walls (U value: 0.4 W/m2K), insulated roof (U value:
0.3 W/m2 K) and high performance glass and
shading for windows. What this has resulted in is an exceptionally low cooling requirement of about 160 TR1 at
peak for a building area of about 15000 m2 (160,000 ft2). High
performance spectrally selective glass (light transmission of 42%,
solar factor of 0.22 and U value of 1.05 W/m2 K) and shading on
windows has ensured that there is ample natural light inside the
building and at the same time occupants feel comfortable without
glare or heat radiation from the windows

Selecting the Right Systems and Efficient Equipment

The second most important step for achieving a high
performance building is to select the most efficient system for the
building. LED lighting is used throughout the building to ensure
low energy consumption and low maintenance due to the long
life of LED lamps. All rest rooms are equipped with motion sensors
that ensure lights are kept off when there is no occupancy The EC-53 building was the first in India to implement a
radiant panel based cooling system. The radiant panels (supplied
by Uponor) are in the form of ceiling tiles and have small pipes
within them through which cold water at 16°C is circulated to take
care of the sensible load in the building. One floor of the building
uses radiant panels developed by the Infosys team to achieve cost
effectiveness and higher cooling efficiency. Air handling units take
care of the latent load in the building and are equipped with two
cooling coils – one with 16°C chilled water and the other with 7°C chilled water.
1TR = 3.517 kW

Other important features of the HVAC system include:
• All equipment with variable speed drives (chillers, pumps,
cooling towers, AHUs).
• Magnetic bearing chillers for high efficiency and low
maintenance.
• Automatic tube cleaning system to ensure chiller efficiency.
• Dual source units (DX + chilled water) for critical areas like
server rooms.
With all these interventions in HVAC, the annual average
efficiency of the chiller plant (chiller, pumps and cooling tower)
was measured to be 0.42 kW/TR

Performance Monitoring

An efficient design does not always translate into efficient
operation if the right metering and performance measurement
is not carried out. The EC-53 building is equipped with a Building
Management System (BMS) with accurate sensors that enable
efficient operation of building systems including proper scheduling
and control of different equipment remotely. The role of the BMS
does not end here. Smart algorithms defined in the BMS make sure
the systems ramp up or down based on the building requirement.
The efficiency of various equipment like chillers and pumps is
continuously tracked with respect to their design curves, and any
deviation is highlighted to enable the operations personnel take
appropriate action. Any critical parameter going out of range
triggers an alarm and notification to the operations personnel
so that any equipment failure can be foreseen and preventive
action taken. Effective use of BMS for control as well as continuous
performance monitoring of the building is a distinguishing feature
of the EC-53 building and several other buildings of Infosys

Solar Energy

The EC-53 building has an installed capacity of 90 kWp solar
PV plant on the rooftop. A unique feature of the plant is that it
consists of 5 different solar technologies of equal capacity on the
same roof. This makes for a very accurate comparison between
 different technologies for the same weather parameters including
temperature, humidity, dust, etc. The technologies installed are
monocrystalline, polycrystalline, HIT, CIS thin film and Cd-Te
thin film. The plant is able to meet about 10% of the energy
requirement of the building on an annual basis

Water Wise

Water is a precious resource, the value of which is inadequately
understood by the society today. Water scarcity is a serious problem
that is increasing every day. When a significant population of the
country does not have access to clean water, it is all the more
imperative to use the available water most judiciously and harvest
every drop of rainwater.
The Infosys EC-53 building has a very low water demand of
25 litre per person per day in all (15 litre fresh water and 10 litre
recycled water), owing to low flow fixtures, dual flush toilets,
waterless urinals, etc. Hundred percent of the wastewater is
recycled in the Sewage Treatment Plant (STP), and the recycled
water is used for flushing, irrigation and cooling tower makeup
requirements. Rooftop rainwater is harvested in a dedicated
tank and used for potable purposes. Last year, about 42% of the
fresh water requirement in monsoon months was met through
rainwater.

Benchmarking Parameters

• Energy Performance index (EPI): 84 kWh/m2 per annum
(includes all the energy consumed in the building) for 100%
daytime occupancy and 50% night time occupancy.
• Building peak electrical load: 2.85 W/ft2 (peak observed at
building incomer in a year).
• Light Power Density (LPD): 0.5W/ft2.
• Peak cooling capacity: 1000 ft2 per TR.
• Chiller plant efficiency: 0.42 kW/TR (annual average).
• Solar PV plant capacity: 90 kWp (meets about 10% of annual
energy requirement).
• Water requirement: 25 litre per person per day.

Conclusion

All the above strategies are replicable for other buildings as
well. The cost of the building is not higher than a regular building.
At Infosys, we have consistently observed that efficient buildings
are less expensive than regular buildings when there is a focus
right from the initial design stage. It only requires a small additional
effort at the design stages and setting the expectations right for
the entire design team. It requires
questioning every assumption
and frugal engineering. It requires
rejecting thumb rules and adopting
a data driven approach. Most
importantly, it requires will from
the entire design team including
the owner to achieve a sustainable
high performance building.

Industrial Dehumidifier Sizing

Introduction

This application note will highlight the primary sources of moisture in industrial facilities. Different methods of solving moisture problems are outlined along with formulas for estimating the moisture content. A questionnaire is incorporated to obtain the minimum information required for proper sizing of dehumidification equipment.

Dry Air

  Quality and productivity are an ever increasing concern for today’s businesses. The effect moisture laden air has on these two concerns is becoming more important as industry strives for tighter operational tolerances. Manufacturers must insure that products maintain specific quality specifications and efficiency is maintained throughout the four seasons.

There are many commercial and industrial applications which require dry air. To eliminate the moisture problem at a reasonable cost, the specifier needs to know how much moisture is present, how did it get in the facility and how to select the proper dehu- midification system.

Methods of Drying Air

There are several methods of drying air. Each method has advantages and disadvantages. The common types are:

            •  Make-up air method

                   •  Compression

                   •  Refrigerated dehumidification

                   •  Desiccant   dehumidification

The fist method uses the principle of dilution, removing a portion of the moisture laden air from a space and replacing it with drier air. The net result is a lower average moisture content. This method is relatively inexpensive to install, but relies on the fact that drier air is available. Since the most common source is outside make up air, this method is difficult to apply in summer months and expensive to operate in winter due to heating costs

Using compression to dry air is effective when small quantities are needed. When air is compressed, the dew point is raised, that is, the temperature at which water vapor will condense is raised. This method has high installation and operational costs and is most common when less than 100cfm of dry air is required

Refrigeration dehumidifiers reduce the moisture in the air by passing the air over a cold surface, removing the moisture by condensation. A detailed discussion on this technique is explained in Desert Aire Technical Bulletin #1. This method is effective for desired conditions down to 45 percent RH for stan- dard applications. Specially designed systems can achieve

dew points as low as 35°F. This method has moderate capital costs and can recover much of the latent energy thus offsetting operating costs.

Desiccant dehumidifiers use special materials that absorb or hold moisture. The material is unique in that it does not change its size or shape when acquiring the moisture and can be regenerat- ed by applying heat. This technique is used effectively to dry air in the range of 0 to 50%RH. It has a relatively expensive capital expense as well as a high operational cost

Sources Of Moisture

There are many sources of moisture in a facility. A list of the Common ones follows:

•  Infiltration • Permeation • Ventilation and make-up air

•  Door and window openings • People • Processes

•  Product

Infiltration and Permeation

Infiltration and permeation are often considered the same thing. Infiltration is the movement of water vapor through cracks, joints and seals. Permeation is the migration of water vapor through materials such as brick and wood. One of the physical laws of nature states that all conditions must be balanced. In the case of water vapor the partial pressure of the water vapor must be the same on either side of a barrier. For this reason water vapor will migrate through brick walls to get to the less humid side. The rate of migration in an unbalanced situation exceeds the rate of air through cracks and seals and will in effect find a path to attempt to balance partial pressures.

Moisture load in a space due to infiltration and permeation is not easily measured. Factors such as the actual moisture deviation, materials of construction, vapor barrier and room size all have an 

effect on the vapor migration. Desert Aire has used some basic models to make assumptions to estimate moisture infiltration and permeation.

The Combined infiltration and permeation load can be approximated from the following equation:

Lb/HR Moisture = V x AC x GR x MF x CF

7000 x 13.5

Where

V     = Volume of room to be conditioned (cu. ft.) AC     = Air change factor from Table 1

DGR = The deviation from the outside to the desired

conditions (grains/LB) 

MF   = Migration factor is DGR ÷ 30 (min. value = 1.0) CF   = Construction factor from table 4

13.5 = Conversion factor for CU. Ft./LB. 7000 = Conversion factor for GR/LB

According to ASHRAE, the median number of air changes per hour is 0.5. The actual number of air changes is influenced by several factors, the most dominate being the size of the room. The larger the room the longer it takes to convert one volume. The following table compensates for the reduction in infiltration

/permeation on larger or smaller volumes

                   VOLUME (CU FT.)      AC                   VOLUME     AC 

                      Less Than 10,000            0.65/HR            40,001-60,000       0.45

                      10,001-20,000               0.60                60,001-100,000          0.4

                      20,001-30,000               0.55              100,000-200,000        0.35

                      30,001-40,000               0.50        Greater  than-200,000       0.3

The rate of infiltration is a function of the magnitude of imbalance between the outside absolute humidity and that inside the conditioned space. The greater the difference, the greater the driving force to make the vapor pressures equal. The migration factor compensates for this influence.

The DGR (grain/lb) deviation must be obtained from the Psychrometric chart. By locating the outside and inside conditions on the chart an absolute humidity in grains/lb can be obtained. The formula uses the difference in grain/lb between these two conditions. Refer to Table 2 and 3 for humidity values for specific locations and inside design conditions. For other values the Psychrometric chart must be utilized. Please refer to Desert Aire Technical Bulletin Number 3 if assistance is required to read the chart.

Another primary factor is the amount of moisture that is allowed to permeate through the walls, floor and roof. The construction factor takes into account the effect good vapor barriers and construction materials will have on the moisture migration.

Table 4 gives factors for common construction materials. This factor will vary between 0.3 and 1.0. A composite wall must be modeled and a factor estimated.

RELATIVE HUMIDITY

	40%	50%	60%	70%
55	25*	32*	40*	45
60	31*	39*	46	54
65	37*	46	55	65
70	42	55	66	78
75	53	66	78	91
80	62	77	93	108
85	72	91	109	128
90	85	108	128	152

DESCRIPTION                               CF FACTOR

Frame construction, no vapor barrier          1.00

Masonry, no vapor barrier                          1.00

Masonic, vapor proof paint                       0.75

Plastic modules                                         0.75

Frame construction, vapor proof paint       0.75 

Frame construction, mylar vapor wrap   0.50 

Sheet metal, good seals                              0.50

Glass                                                          0.30

Door Openings

Another source of moisture is the opening of doors and windows to the conditioned space or other openings such as conveyor passages. In these cases, the amount of moisture is directly proportional to the frequency of the opening, the difference in indoor and outdoor moisture con- tent and the wind velocity at the opening. The wind velocity will be the most difficult to take

into account since it will vary depending on the location of the opening with respect to the wind source. Local weather stations can provide details on the normal prevailing direction and speed. However, a guideline is 12 CFM of outside air per square feet of opening.The amount of air can be estimated by the following formula.

LB/HR = AREA x OPEN x DGR x 12

7000 x 13.5

Where:

AREA = Surface area of opening ( Sq. Ft.) OPEN = Minutes area is open per hour

DAG = The deviation from the outside to the

desired conditions (grains/LB)

12      = Estimated ingress of moisture (CFM/Sq.Ft.)

13.5 = Conversion factor for CU.FT./LB 7000 = Conversion factor for GR/LB

When this equation is used for a fixed opening such as a window, the minutes open/hr will equal 60.

Product, Process and People

The three “P’s”, product, process and people must also be included in the moisture evaluation. If the product has an affinity for water, then it may also release the water in the conditioned room. For example, wet wood brought into a conditioned warehouse will release the water at a specific rate. This can be determined by measuring the products weight loss over time.

The process itself may generate moisture. If there are open watertanks or cooking vessels, they will add moisture. A model must be developed for each process

In the case of, open water tanks, the evaporation rate can be calculated with the following equation.

LB/HR =      0.1 x AREA x (VPH2O - VPAIR)

Where:

Area       = Surface area of water (square feet).

VPH2O       = Vapor pressure of water at water temperature VPAIR           = Vapor pressure of air at it’s corresponding

dew point.

The above equation assumes 10 to 30 FPM air velocity in room. Vapor pressures can be obtained from technical publications. Consult Desert Aire if you need assistance. Finally people give off moisture. This is a function of the number of people and their activity: a worker lifting boxes will generate 4 to 8 times the moisture of a worker at a lab bench. ASHRAE’S data on the amount of water added per person is reproduced in table 5.

      Ventilation and Make-up Air

If the facility is using fresh outside make-up air for ventilation as required by some building codes, then this air can contribute to the moisture load. This is especially important in the summer months when high humidity is common. As with the calculation for infiltration the difference in absolute humidity must be used, along with the volume of make-up air being brought in by the air handling system. The formula for calculating moisture load is:

LB/HR Moisture = CFM x DGR x 60 

                                 7000 x 13.5

CFM =        Volume of outside air introduced

DGR =                 The deviation from the outside to the desired conditions (grains/LB)

60     =       Conversion factor for min/hr

13.5  =        Conversion factor for CU.FT./LB 7000 =        Conversion factor for GR/LB

Conclusion

To properly select and size a dehumidification system to condi- tion a facility requires careful planning. The engineer or facility operator must specify the operating conditions that must be maintained. Then he must evaluate all of the potential sources of water and the outside ambient conditions. This information can then be used to size the system. The enclosed worksheet

is provided to organize the collection of minimum information required for selection and sizing. The formulas will provide an approximation of the moisture load. An engineer should be consulted to confirm that the assumptions are appropriate for the application